Data backup including tape and non-volatile memory units and method of operating same

ABSTRACT

A tape drive assembly for performing a backup operation has a tape receiving station to receive a data storage unit including a tape to store data in a data backup operation. A write head writes data to the tape in a data backup operation. A non-volatile memory unit records data in a data backup operation and communicates data to the write head. An input connected to a data host machine passes data to the memory unit such that, in use in a data backup operation, the data are communicated from the data host machine to the input and recorded in the memory unit prior to the data being passed from the memory unit to the write head for writing to the tape.

FIELD OF THE INVENTION

This invention relates to data backup methods, and to data backupdevices.

BACKGROUND OF THE INVENTION

It is common for an organisation to wish to securely and quickly savedata, for example transactional data, or changes to data made during aperiod. A backup data copy is created in case the primary data file isdamaged in some way or is lost. In many organisations this is done bycopying a database/data records to tape in a separate, often overnight,data backup operation, typically whilst users are not altering the data.It is also common to have backup data records deliberately stored at adifferent geographical site than that at which the primary data file isstored. For example, backup tapes may be taken home with seniorinformation technology (I.T.) staff, or a backup data record may be madeover a wide area network (WAN) to keep it in a different physicallocation.

For some organisations there is a difficulty in reliably backing uptheir overnight data. If the volume of data to be backed up is large(and sometimes it could be 50 GB or more) it might take something of theorder of 4 hours or so to back it up onto tape. Some organisations mayhave a long working day: for example from 6.00 a.m. to 10.00 p.m. Thisleaves only 8 hours to perform the backup. This is usually long enough.However, if there is a problem backing up the data the backup can runout of time to complete the backup operation before organisation wishesto start changing the original data again. For example, if a tape driveperforms two hours of a backup operation and then starts to get repeateddata error signals it may cancel that backup and start again. If thishappens again (and possibly again) then no backup may have beencompleted by the time that the organisation opens for business the nextmorning. This leaves the I.T. manager with a choice: deny personnelaccess to their computers (or at least those functions that will alterthe data being backed up until the backup is complete), or allow the“live” data to be modified without there being a backup of the previousday's data/changes to the data.

The first option is hardly ever attractive. The second option is alsonot attractive, but is often the only practical possibility.

Possible solutions to this problem include manning the backup facilityovernight so as to have human intervention/input to problems (mostovernight backups are performed with no humans present to oversee them),but this is not popular with the people involved.

Another possibility is to make the backup operation faster so that morere-tries are possible in any given period.

There is a common drive in service provider computer environments toarchitect the I.T. infrastructure to avoid having a single point offailure. Current tape library arrangements, for example in the backupscenario described, are not fault tolerant. The tape drive is often asingle point of failure. If there is a problem with the tape drive thenthe whole data storage tape library fails. It is known to avoid this byusing RAIT technology (Redundant Array of Inexpensive Tapes). However,the “inexpensive” part of RAIT is a misnomer: having multiple tapedrives, each with their own array of tapes and an automatic tapechanger, is very expensive. Furthermore, if a backup is distributed overseveral tapes there is then a need to keep a set of tapes together: toassociate them in some way. This also is inconvenient for the persontaking out of the building the backup tapes since they now have a bundleof tapes.

Tape is the preferred medium for storing backup data because it ischeap, robust, and can be removed from the tape drive and re-insertedmany times. Tape cassettes can withstand the treatment given to them(e.g. put in a bag or case, thrown in the car, driven around/shook up,left in warm/cold environments) and still be inserted/removed from atape drive very many times before the insertion/removal operation, orsimply their use once inserted, wears them out. They can also store alot of data.

Floppy discs can be inserted/removed from a disc drive, but they areless robust, and may not withstand the insertion/reinsertion so manytimes, and currently cannot store so much data.

Whilst removable hard discs exist, they are very expensive and are lessrobust, and are not designed for regular, repeated, insertion/removalevery day for a year, or years.

Furthermore, if a tape physically breaks it is often possible to readdata at regions of the tape away from the break. If a disc physicallybreaks that is far from easy to do (if it is possible at all). Thustapes also have a greater chance of being able to have data recoveredfrom them in the event of a physical accident to the data carrier.

A number of prior art arrangements of data protection are known, see forexample JP 1100102262, where data stored in a hard disc at a main hostcomputer is stored on an off-site tape library. JP 580144270 discussesanother data storage device. WO 90/06580 deals with a tape drive and adisc drive mounted in the same housing having common control circuitry.Also, U.S. Pat. No. 5,822,184 shows a tape and disc drive being mountedin the same housing.

U.S. Pat. Nos. 6,161,169 and 5,805,921 disclose bus/buffer managementalgorithms and techniques.

SUMMARY OF THE INVENTION

It is an aim of the present invention to provide an improved method orapparatus for data storage, data backup, and/or data recovery.

According to a first aspect, the invention comprises a tape driveassembly for performing a backup operation, comprising:

-   -   a tape receiving station arranged to receive a data storage unit        including a tape arranged to store data in a data backup        operation;    -   a write head arranged to write data to said tape in a data        backup operation;    -   a non-volatile memory unit adapted to record data in a data        backup operation and adapted to communicate data to said write        head;    -   an input adapted to be connected to a data host machine; said        input being arranged to pass data to said memory unit such that,        in use in a data backup operation, said data is communicated        from said data host machine to said input and is recorded in        said memory unit prior to said data being passed from said        memory unit to said write head for writing to said tape.

According to another aspect of the present invention there is provided atape drive assembly comprising:

-   -   a tape receiving station arranged to receive a data storage unit        including a tape arranged to store data;    -   a write head arranged to write data to said tape;    -   a non-volatile memory unit adapted to record data and adapted to        communicate data to said write head;    -   an input;    -   said input being arranged to pass data to said memory unit such        that, in use, said data is recorded in said memory unit prior to        said data being passed from said memory unit to said write head        for writing to said tape.

The memory unit may be a hard disc. The hard disc may have a datastorage capacity of the order of any of the following figures, or ofbetween any pair of the following: 25 GB, 50 GB, 75 GB, 100 GB, >100 GB,of the order of TB, or more. Alternatively, the memory unit may be asolid state device, for example SRAM, E²PROM or flash card. The memoryunit may be a log.

This allows a short term, typically a few hours, backup of the completedataset to be made to a non-volatile storage medium from which data canbe recovered (e.g. to tape or indeed to recover a system from the dataheld therein) should the backup to tape fail.

There may be a processor, which may be arranged to control the passageof data to the write head and the memory unit. The processor may besituated within or nearby the tape drive assembly. The processor may bearranged to replicate the data and the data may be passed to the writehead and the memory unit in parallel. Alternatively, the data may bepassed to the write head and the memory unit, or vice versa, inseriatim.

There may be a plurality of memory units. The memory units may bearranged in a redundant array of inexpensive (RAI) memory units, wherethe memory units are discs, this may be a RAI Discs (RAID) arrangement.

The memory elements may be arranged to mirror data recorded thereupon,in use, for example discs in a RAID 1 arrangement.

There may be an output from the memory unit. The output may be arrangedto allow the download of data stored within said memory unit. A datastorage device may be arranged to receive said stored data. The storagedevice may be a tape unit, which may be received in said receivingstation. Alternatively a server, or a terminal (e.g. a P.C) may bearranged to receive said stored data

The tape drive assembly may form part of a tape library. The tapelibrary drive may include a plurality of tape drive assemblies. Theremay be a plurality of tape data storage units associated with said tapelibrary. There may be a tape changer arranged, in use, to remove andinsert tapes from the tape drive assembly. Said tape changers may bepart of said tape library. The tape changer may be adapted to change atape automatically. There may be tens of tapes, or more, in the tapelibrary for each tape drive assembly.

There may be a multiplexer. The multiplexer may be arranged to multiplexincoming data signals either before or after the signals have beenwritten to the non-volatile memory element, in use.

The assembly may be arranged to issue a warning should either or both ofthe memory unit or the tape drive fail. The warning may be audible or itmay be visual. The assembly may be arranged to issue a warning to aremote management console, typically via a network.

According to another aspect the invention comprises a method of backingup data stored on a host data-containing machine comprising the stepsof:

-   -   i) receiving data from said host machine at an input of a tape        drive assembly;    -   ii) passing said data to a non-volatile memory unit;    -   iii) routing said data through said memory unit and recording        said data in said memory unit;    -   iv) passing said data to a write head of said tape drive        assembly; and    -   v) attempting to write said data to a tape data storage medium        to backup said data to said tape data storage medium.

Steps ii) and iii) and steps iv) and v) of the method may be executedsubstantially simultaneously. Alternatively, steps ii) and iii) of themethod may be executed in seriatim with steps iv) and v), or vice versa.

The method may include storing the data in the memory unit as a buffer.The method may include recovering the data from the memory unit shouldthe data not be successfully written to the tape.

The method may include executing steps iv) and v) of the method only ifstep iii) Should fail, possibly only if step iii) should fail. Themethod may include executing a step of read after write dataverification after step iii). This may serve to determine if step iii)has failed or not.

The method may include establishing a data set to be backed up andexecuting steps ii) and iii) until all of said data set to be backed upis stored upon said memory unit.

The method may include allowing random, or multi-point, access to thememory unit. This may enable access to and/or export of a selectedportion of the stored data, preferably without having to run the portionof the data storage medium past the read head prior to reading/exportingthe selected portion. The method may include selecting a portion of thestored data to be accessed/export in response to an automated, or userinput, signal.

The method may include providing the memory unit in the form of a harddisc. Alternatively, the method may include providing the memory unit inthe form of a solid state device, for example SRAM, E²PROM or flashcard.

The method may be performed in conjunction with a control processor andthe tape drive assembly may include said memory unit as an integral unitor a combined assembly, and a control processor may be associated withsaid memory unit or said tape drive assembly. In such an arrangement,the control processor receives a backup operation initiation signal, andupon receipt thereof causes a backup operation to be performed, therebybacking up said data.

The method may include controlling the passage of data to the write headand the memory element with said processor.

The method may include providing a plurality of memory units, possiblyin an RAI arrangement. The method may include mirroring the data writtenupon said plurality of discs/RAI memory units.

The method may include providing an output from the memory unit. Themethod may include allowing the download of data stored within thememory unit. The method may include providing a data storage devicearranged to receive said stored data. The method may be performed in asystem in which said data storage device is in the form of a tape andincludes a server, or a terminal (e.g. PC), arranged to receive saidstored data.

The method may include multiplexing data either before or after it hasbeen written to the non-volatile memory unit.

The method may comprise overwriting data previously stored in saidnon-volatile memory unit from an earlier backup operation with data froma later backup operation.

The method may further comprise

-   -   determining if a problem has been detected indicating that        backup to said tape data storage medium has failed to be        achieved properly;    -   if no determination of backup to tape data storage medium has        failed to be achieved properly in the immediately preceding        step, a subsequent backup operation is allowed to overwrite data        stored in said non-volatile memory unit from a previous backup        operation with data from said subsequent backup operation.

The method may further comprise:

-   -   inserting another tape into said tape drive;    -   determining if data was successfully backed up to tape during        said first backup routine;    -   performing a second backup routine, subsequent to said first        backup routine and after said data set in said host machine has        changed; and    -   overwriting data stored in said non-volatile memory element        during said first backup routine with a new data set from said        host machine during said second backup routine, said second        backup routine also writing said new data set to said another        tape.

The method may comprise performing a specific backup operation andensuring that said non-volatile memory unit has a large enough capacityto store an entire data set that is to be backed up in said backupoperation.

Preferably said non-volatile memory unit has a large enough capacity tostore at least two data sets from at least two successive backupoperations, or possibly 3, 4, 5, 6, 7, or more backup data sets.

The method may be performed on a data set to be backed up of a generallyknown predetermined size and in a non-volatile memory unit large enoughto store the whole of data from a plurality of back up operations. Insuch a situation, a plurality of successive backup operations of saiddata set are stored in said non-volatile memory unit; and earlierbacked-up data are overwritten with new backup data in a first-in-firstout manner when there is otherwise insufficient capacity in saidnon-volatile memory unit to accommodate data from a new backupoperation.

According to another aspect the invention comprises a backupnon-volatile memory unit comprising a discrete stand-alone unit arrangedfor use with a tape drive, said assembly further comprising:

-   -   a non-volatile memory element;    -   an input port;    -   an output port;    -   said assembly being arranged to receive data via said input        port, store said data to said non-volatile memory element, and        output said data via said output port to said tape drive.

The input and output port may be combined as an input/output (IO) port.The assembly may include a processor. The processor may be arranged tocontrol the writing of the data to the memory element, in use. Theprocessor may be arranged to control the reading of the data from thememory element, in use. The processor may have a buffer. The buffer maybe arranged to store the data temporarily, typically for a few ms, inuse. The processor may be arranged to control the flow of data throughthe assembly, in use. The processor may be arranged to output some orall of the data, in use.

The non-volatile memory element may be a hard disc. There may be aplurality of hard discs. The hard discs may be arranged in a RedundantArray of Inexpensive Discs 1 (RAID 1) arrangement. The hard discs may bearranged in a RAID level that provides fault tolerance, for example RAID1, 3, 5 . . . Alternatively, the non-volatile memory element may be asolid state device, for example SRAM, E²PROM or flash card, or anoptical element, such as an optical disc. The non-volatile memoryelement may be arranged to be removed from the assembly, in use. Thenon-volatile memory element may be a log.

The assembly may have a power supply which may be independent of thetape drive or tape library. The power supply may have a surge protector.The assembly may have a reserve power supply. The reserve power supplymay be internal of the assembly. The reserve power supply may be abattery.

There may be provided a multiplexer. The multiplexer may be arranged tomultiplex data either before or after it has been written to thenon-volatile memory unit, in use.

The assembly may be arranged to issue a warning should either or both ofthe memory element or the tape drive fail. The warning may be audible orit may be visual. The assembly may be arranged to issue a warning to aremote management console, typically via a network.

According to another aspect of the present invention there is provided amethod of backing up data with a backup arrangement including a tapedrive with associated removable tapes and a non-volatile memory element,wherein the method comprises the step of writing data to be backed up toboth the tape and non-volatile memory element.

Preferably the tape is removed from the tape drive after completion ofthe backup.

The method may comprise the step of using the non-volatile memoryelement as a local backup. The method may comprise the step of using thetape as a remote backup.

The method may be performed with a plurality of hard discs arranged in aRedundant Array of Inexpensive Discs 1 (RAID 1) arrangement and whereinthe non-volatile memory element is in the form of a hard disc. In such asituation, the method may comprise the step of arranging the hard discsin a RAID level that provides fault tolerance, for example RAID 1, 3, 5.Alternatively, the method may comprise the step of providing thenon-volatile memory element in the form of a solid state device, forexample SRAM, E²PROM or flash card. The method may comprise the step ofproviding the nonvolatile memory element in a removable form, in use.

The method may include multiplexing data either before or after it hasbeen written to the non-volatile memory unit. The method may comprisethe step of retrieving the data from the non-volatile memory unit. Themethod may comprise the step of allowing access to a selected portion ofthe data stored on the non-volatile memory unit. The method may comprisethe step of retrieving data stored upon the tape, typically if retrievalfrom the non-volatile memory element fails.

Both of the prior art arrangements discussed hereinafter result in thegeneration of two tape copies of the backed up data. One for ‘offsite’storage for data security, for example, in the case of fire and one foreasy ‘onsite’ usage. The present invention allows for the same result tobe achieved but with the generation of only a single tape copy for‘offsite’ storage. The onsite backup storage is typically provided by a“captive” memory unit that is not usually removed/removable from thedata backup unit.

The method may include issuing an interrupt and commencing the writingof the data to the memory unit if a signal indicative of a backupstarting is received.

According to another aspect of the present invention there is provided anetwork comprising a data source, a tape drive assembly and a backupnon-volatile memory element.

The non-volatile memory element may be a hard disc. The non-volatilememory element may be internal of and/or integral with the tape driveassembly, in accordance with the first aspect of the present invention.Alternatively, the non-volatile memory element may be a non-volatilememory assembly provided separately from the tape drive assembly.

The data source may be any one, or combination, of the following: a hostcomputer or machine hosting a database, a network, a disc array, a tapedrive, a tape library, a server, a terminal (such as for example a PC)or a network switch (for example fibre channel or Ethernet).

The combination of the tape drive and the non-volatile memory elementmay operate according to a previously defined method aspect of thepresent invention. The non-volatile memory assembly may operateaccording to a previously defined method aspect of the presentinvention.

According to another aspect the invention comprises a network withelements connected to be responsive to a data source having a data setto be backed up. The elements include a backup unit comprising a tapedrive assembly having a read/write head and a backup non-volatile memoryelement of a capacity such as to be able to accommodate at least onecopy of said data set. The tape drive assembly and memory element are ina Common unit having an input communicating with said data source and anoutput adapted to output data obtained from said tape drive assembly andadditionally or alternatively from said memory element. The inputcommunicates data coming from said data source with said memory elementfor storing said data set at said memory element. The memory elementcommunicates with said tape drive assembly to write said data using saidread/write head to a tape located in said tape drive.

According to another aspect the invention comprises a network comprisinga data source having a data set to be backed up, and a backup assemblycomprising a tape drive assembly and a non-volatile memory unit. Thenon-volatile memory unit comprises:

-   -   a non-volatile memory element of a capacity such as to be able        to accommodate at least one copy of said data set;    -   a unit input port; and    -   a unit output port.

The nonvolatile memory unit is arranged to (1) receive data via saidunit input port from said data source, (2) store said data set to saidnon-volatile memory element, and (3) output said data set via set unitoutput port to said tape drive assembly.

According to another aspect of the present invention there is provided atape library comprising at least one tape drive, at least onenon-volatile memory element and a plurality of tape data storage units.

The non-volatile memory element may be a hard disc. The non-volatilememory element may be internal of and/or integral with the tape driveassembly, in accordance with the first aspect of the present invention.Alternatively, the non-volatile memory element may be a non-volatilememory assembly provided separately from the tape drive assembly, inaccordance with at least part of the third aspect of the presentinvention.

The combination of the tape drive and the non-volatile memory elementmay operate according to the method of second aspect of the presentinvention. Alternatively, the non-volatile memory element may operateaccording to the method of the fourth aspect of the present invention.

The tape library may comprise a tape autochanger arranged to insert onethe plurality of tapes into and remove one of the plurality tapes out ofthe tape drive, in use.

According to another aspect of the present invention there is provided amethod of operating a non-volatile backup assembly including anon-volatile memory unit having a non-volatile memory element, an inputand an output; comprising the steps of:

-   -   i) connecting the output to an input of a tape drive assembly;    -   ii) receiving data at the input from a data source;    -   iii) copying the data to the non-volatile memory element; and    -   iv) outputting the data from the output to the tape drive        assembly.

The method may include the step of releasably connecting the memory unitto the tape drive assembly, wherein the memory unit is locatedinternally or externally of the tape drive assembly. The method mayinclude downloading the data from the memory unit to a different tapedrive from that to which the data was output. The method may includeproviding the non-volatile memory assembly in accordance with the thirdaspect of the present invention.

According to another aspect the invention comprises a method ofperforming a backup operation with a non-volatile backup unit having anon-volatile memory element, an input and an output; the methodcomprising:

-   -   i) connecting said output to an input of a tape drive assembly;    -   ii) receiving data at said input from a remote data source;    -   iii) copying said data to said non-volatile memory element; and    -   iv) outputting said data from said output to said tape drive        assembly.

Another aspect of the present invention relates to software which runson a processor of a backup system including both a tape drive, having adata storage medium mounted therein, and a non-volatile memory element.The software is arranged to (1) access data being backed up and (2) copythe data to both the data storage medium and the non-volatile memoryelement, in use.

The software may be arranged to allow access and/or retrieval of thedata from either or both of the data storage medium and the non-volatilememory element, in use.

The non-volatile storage element may be a hard disc. There may be aplurality of hard discs and they may be arranged in a fault tolerantRAID configuration, for example RAID 1, 3, 5

According to further features of the present invention there areprovided a method of increasing the speed of access to specific backedup data; and a method of increasing the reliability of a backup.

According to any preceding aspect of the present invention it ispreferable that the backup occurs without human intervention (at leastafter it has been initiated).

It will be appreciated that fault tolerance is a desirable feature inany system and accordingly there may be redundancy, typically in theform of reserve components, incorporated into the tape drive assembly,tape library, or non-volatile memory assembly, or element according tothe preceding aspects of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described, by way of example only, with referenceto the accompanying drawings in which:

FIG. 1 is a schematic representation of a prior art arrangement forperforming a data backup to tape;

FIG. 2 is a schematic representation of a prior art RAIT arrangement forperforming a data backup to tape;

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FIG. 3 is a schematic representation of a first embodiment of a tapedrive assembly in accordance with an aspect of the present invention;

FIG. 4 is a schematic representation of a second embodiment of a tapedrive assembly in accordance with an aspect of the present invention;

FIG. 5 is a schematic representation of a tape library comprising tapedrive assemblies in accordance with an aspect of the present invention;

FIG. 6 is a schematic representation of a first embodiment of amultiplexing tape drive assembly in accordance with an aspect of thepresent invention;

FIG. 7 is a schematic representation of a second embodiment of amultiplexing tape drive assembly in accordance with an aspect of thepresent invention;

FIG. 8 is a schematic representation of a first embodiment of a standalone non-volatile memory unit in accordance with an aspect of thepresent invention adapted for use with a tape drive;

FIG. 9 is a schematic representation of a second embodiment of a standalone non-volatile memory unit in accordance with an aspect of thepresent invention adapted for use with a tape drive;

FIG. 10 is a schematic representation showing a non-volatile memory unitof either of FIG. 8 or 9 in use;

FIG. 11 is a flow diagram detailing a method of data backup inaccordance with an aspect of the present invention;

FIG. 12 is a flow diagram detailing an alternative method of data backupto that of FIG. 11 in accordance with an aspect of the presentinvention;

FIG. 13 is a flow diagram detailing a method of data retrieval inaccordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

It will be appreciated that the description of the preferred embodimentsof the present invention is exemplary only and is intended to provide athorough understanding. It will be further appreciated by one skilled inthe art that the present invention may be executed without limitation tothe embodiments described hereinafter and that well known methods andstructures have not been described hereinafter, so as not tounnecessarily obscure the present invention.

Referring now to FIG. 1, which shows a prior art arrangement forperforming backups of data from a data source 10, a tape drive 11comprises a housing 12, a tape receiving bay 14, a plurality of tapes 16a-g a tape changer 17 a read/write head 18, and a buffer 19.

During a backup data is passed between the source 10 and the drive 11via a data link 20. The data link 20 is typically a SCSI connection or afiber channel connection.

A tape 16 a is placed in the receiving bay 14 and initialised. Whenbackup commences data is passed over the data link 20 to the write head18 via the buffer 19 and is written to the tape 16 a. The data can beverified in the normal way. However, should a fault develop within thetape drive 11 the data source 10 will continue to produce data eventhough it is not being recorded to the tape and thus a portion of theduration of a backup will be lost. This arrangement presents the tapedrive 11 as a single point of failure.

FIG. 2 shows a prior art attempt to reduce the likelihood of a singlepoint of failure of the backup occurring at any single tape drive knownas a redundant array of inexpensive tapes (RAIT). In the arrangement ofFIG. 2 a four tape drives 11 a-d are connected to a control unit 22 byeach of three independent data links 24 a-c. The control unit 22,typically a slot in card or systems software, receives data from thesource 10 and, in this instance, replicates the data. The replicateddata is passed via all three of the data links 24 a-c to each of thewrite heads 18 a-d. Thus, should any one component of the RAITarrangement fail the backup can usually complete with at least onebackup of the data being successfully completed. The problem with thissolution is that the term, inexpensive, is a misnomer, as although thetapes themselves are inexpensive the tape drives are not.

FIG. 3 shows a first embodiment of the present invention, in which atape drive assembly 26 comprises a housing 28, a read/write unit 30, aplurality of tapes 32 a-f, a tape auto-changer 34 and a non-volatilememory unit 36. The memory unit 36 comprises two mirrored hard discs 38a, 38 b and a processor 40.

A server 42 has backup software 44 running on it and is connected to thedrive assembly 26 via a data link 46. The data link 46 is typicallyeither a fiber channel or SCSI connection.

The backup software 44 initiates the backup of data stored on the server42 and data is transferred over the data link 46 to the drive assembly26. The data is passed to the processor 40 where it is replicated. Onecopy of the data is passed to the read/write unit 30 as will bedescribed hereinafter. A copy of the data is written to each of themirrored hard discs 38 a, 38 b, i.e. the discs are in a RAID 1arrangement. The discs 38 a, 38 b will typically each have sufficientdata storage capacity to store the total amount of data transferredduring the backup.

However, if an extremely large amount of data is to be backed up and itis not possible to contain all of the data on a single disc, theprocessor 40 may switch the discs 38 a, 38 b from a RAID1 configurationsuch that one of the discs (for example, disc 38 a) is filled with data,and then the other disc 38 b is filed sequentially. Alternatively, theprocessor 40 can partition the data into segments, allocate the segmentsto either disc and generate a log of where each segment of data islocated. This allows particularly important data to be written to bothdiscs as an extra safeguard. This important data will have a flag whichis set by the backup software 44, for example, a vendor unique SCSIcommand, and recognised by the processor 40.

The read/write unit 30 has one of the tapes 32 a therein and data passedfrom the non-volatile memory unit 36 is written to the tape 32 a in theconventional manner. The transcription of the data to the tape 32 a isverified in a conventional manner. Should the tape 32 a become overfull,or fail, the autochanger 34 changes it for another tape 34 f, forexample, that has spare data storage capacity and has not failed.

The discs 38 a, 38 b may be large enough to hold enough data toaccommodate several data sets (sets of data to be backed up as a back-uprecord of a database/record on a host system). For example, a week'sworth of daily backups may be simultaneously stored on the discs 38 a,38 b. However, eventually it will be necessary to overwrite a previousbackup record data set with a new backup data set. Typically, the oldestprevious data set(s) will be overwritten.

In an alternative arrangement the tape drive assembly 26 datatransferred to the assembly 26 is replicated and one copy of the data istemporarily retained by the processor 40 in a buffer region 40 a. Afurther copy of the data is forwarded to the read/write unit 30.

The read/write unit 30 attempts to write the data to the tape 32 a inthe conventional manner. The unit 30 attempts to verify the data in theconventional manner. Should the verification attempt fail a signal 46 issent to the memory unit 36 which instructs the processor 40 to commencewriting the data to the discs 38 a, 38 b. The copy of the data stored inthe buffer 40 a will be the first data block to be written to the discs.Thus, the tape 32 a contains all of the data up to the point of failureof the tape drive arrangement and the discs 38 a, 38 b contain theremainder of the backed up data.

If the data recording to the tape is successful the data written to thebuffer region 40 a may be overwritten with new data. Alternatively abackup to disc may be taken automatically, irrespectively of whether thebackup to tape is successful.

The discs 38 a, 38 b will typically have sufficient storage capacity tostore the entire backup (or several backups, or many backups) in amirroring, RAIDed, arrangement. Alternatively, the processor 40 canpartition and allocate the data between the two discs 38 a, 38 b asdetailed hereinbefore.

The plurality of tapes 32 b-f and the autochanger 34 operate in the samemanner as in the previously described arrangement.

Referring now to FIG. 4 this shows a second embodiment of the presentinvention comprising a tape drive assembly 50 connected to a server 52via a data link 54.

The tape drive assembly 50 comprises an non-volatile memory unit 56 anda tape read/write unit 58 connected via a single connector 59. Theread/write unit is shown with a tape 60 therein. The memory unit 56comprises a plurality of non-volatile memory elements 62 and a processor64. The memory elements 62 will typically be hard discs although theymay include solid state devices such as E² PROM, SRAM or flash memory.

The server 52 initiates a backup routine and data is transferred fromthe host machine, or server 52 to the drive assembly 50 via the datalink 54. The data is handled in the same fashion as describedhereinbefore for the first embodiment.

FIG. 5 includes a tape library 66 comprising a plurality of tape driveassemblies 26 a-d as described in relation to the first embodiment.

FIG. 6 shows an alternative arrangement of a tape library 68 in which aplurality of input/output lines 70 a-d each have their own non-volatilememory unit 72 a-d. The output from each of the memory units 72 a-d isfed to a multiplexer 73 where it is multiplexed. A single multiplex datalink 74 links the multiplexer 73 to a tape drive 76. The tape drive 76is the same as that described hereinbefore in relation to the firstembodiment.

FIG. 7 shows a further alternative embodiment of a tape library in whichmultiple data input/output lines 78 a-d enter a multiplexer 80. Theoutput from the multiplexer 80 is passed to a tape drive assembly 26 ashereinbefore described.

Referring now to FIG. 8, a stand-alone memory unit 82 intended to be anadd-on peripheral for current tape drives, comprises an input/outputport 84, a processor 86, a RAID distributor board 88, two hard discs 90a,b, two read/write heads 92 a,b, a power input socket 94 and a battery96.

The input/output port 84 is arranged to receive data from a data source,typically a host machine or computer which stores the data and whichusers of the host machine access during live use of the data by, forexample, a business. A typical data source could be a server, or anetwork. The port 84 is also arranged to transmit data to a connection—atape drive.

The RAID board controls the mirroring of the data and also the possiblepartitioning of the data in conjunction with the processor 86.

The processor 86, hard discs 90 a,b and read/write heads 92 a,b operateas described hereinbefore.

The power input socket 94 receives power either from an a.c. supply, inwhich case a transformer is an integral part of the socket 94.Alternatively, the socket 94 receives power from a d.c. supply, such asan external transformer or battery pack. The battery 96 acts as a backuppower supply should the supply from the socket 94 be interrupted.

The battery 96 will typically have a long enough lifetime to maintainthe utility of the memory unit 82 until the power supply via the socket94 can be re-established.

An optional, additional, output port 98 is shown ghosted. The additionaloutput port 98 can be used to output the data to a second tape drive orto a network.

Referring to FIG. 9, an alternative arrangement of a stand-alone memoryunit 100 arranged to be connected to a standard tape drive via astandard input or input/output arrangement comprises an input/output(IO) port 102, a non-volatile element 104, a processor 106, a powerinput 108, a battery 110 and an output port 112.

A data link 114 connects the IO port 102 directly to the memory element104. A data link spur 116 is tapped from the data link 114 directly tothe output port 112. This increases the speed of operation of thearrangement as no processing of data occurs prior to the transcriptionof the data to tape via the tape drive assembly. The processor 106controls the writing of data to the memory element 104.

The output port 112 is connected via a lead or infra-red link to a tapedrive.

Referring to FIG. 10, this shows a stand-alone memory unit 118 connectedto a data source 120, typically either a server or a network, and a tapedrive 122.

The stand-alone memory unit 118 is releasably connected to both the tapedrive 122 and the data source 120. The connections can be effected bycables with suitable heads such as Ethernet, SCSI, or fibre channelcables. Alternatively the connection may be effected by infra-red orradio frequency data links.

FIG. 11 is a flowchart detailing the process of backing up dataincluding backing data up to non-volatile memory.

The server generates signals (step 124). These signals are typicallystandard input/output signals such as SCSI commands. The tape driveprocessor receives the signals from the server via a data link andinterrogates them to see if a “backup starting” signal is present inthem (step 126), for example a rewind to start of media command followedby a write command.

If a “backup starting” signal is not contained in the server generatedsignals the tape drive continues to interrogate the incoming signals.However, should a “backup starting” signal be registered by theprocessor logging of the data and commands by writing it to anon-volatile memory element (step 128). The memory element is typicallya hard disc or a solid state memory device and will typically bemirrored in another memory element.

The arrangement checks to see if there has been a tape or tape drivefailure (step 130). If no failure is noted the data and commands arewritten to a tape in the tape drive assembly (step 132) and theinput/output signals from the server are interrogated by the processorto ascertain if the backup is still in progress (step 134). Should theprocessor receive a termination of backup signal from the server thelogging of data and commands to the memory element is terminated (step136). If no termination of backup signal is registered by the processorthe process returns to checking for a tape drive or tape failure (step132).

Should a tape drive, or tape failure occur and be logged (step 132) thedrive assembly will issue a failed peripheral signal (step 138) tonotify a user of the system that the failure has occurred. In a systemwhere a tape autochanger is provided, along with an array of tapes, thedefective tape will be removed from the tape drive and replaced by analternative, non-defective, tape (step 140).

In an alternative arrangement no check to see if there has been a tapeor tape drive failure (step 130) as the incoming data is logged directlyto the nonvolatile memory unit as well as being written to tape.

It will be appreciated that should a tape drive or tape failure beregistered the memory element continues to log all the data and commandsemanating from the server for the duration of the backup irrespective ofwhether an autochanger is provided or not.

FIG. 12 is a flow chart detailing an alternative method of data backup.The server generates signals (step 142). These signals are typicallystandard input/output signals such as SCSI commands. The tape driveprocessor receives the signals from the server via a data link andinterrogates them to see if a “backup starting” signal is present inthem (step 144).

If a “backup starting” signal is not contained in the server generatedsignals the tape drive continues to interrogate the incoming signals.However, should a “backup starting” the arrangement checks to see ifthere has been a tape or tape drive failure (step 146). If no failure isnoted the data and commands are written to a tape in the tape driveassembly (step 148). However, if a tape or tape drive failure signal isregistered by the processor logging of the data and commands by writingit to a nonvolatile memory element (step 150) commences. The memoryelement is typically a hard disc or a solid state memory device and willtypically be mirrored in another memory element.

The drive assembly will issue a failed peripheral signal (step 152) tonotify a user of the system that the failure has occurred. In a systemwhere a tape autochanger is provided, along with an array of tapes, thedefective tape will be removed from the tape drive and replaced by analternative, non-defective, tape (step 154).

The input/output signals from the server are interrogated by theprocessor to ascertain if the backup is still in progress (step 156).Should the processor receive a termination of backup signal from theserver the logging of data and commands to the memory element isterminated (step 158). If no termination of backup signal is registeredby the processor any data and commands output from the server continueto be logged.

FIG. 13 is a flowchart detailing the process of data recovery from anon-volatile memory element. The necessity to recover data from thememory element is realised (step 160). This will typically be due to abackup failing to complete due to a tape failure as for example abreakage or loss of formatting information. Alternatively, it may be dueto a tape drive failure for example a motor failure, a damage or failureof a read/write head or the partial or intermittent failure of aninput/output line.

A data retrieval command is issued to the processor that controls thememory element (step 162). This may be an automated system command or itmay be a user-generated command. The data retrieval command willtypically relate to part of the data stored on the memory element aspart of it will usually be recoverable from the tape. For example, ifthe tape drive fails two hours into a five-hour backup it may only benecessary to recover the least three hours' worth of data from thememory element. However, there may be circumstances such as the tapebecoming irreparably damaged, for example fire, or the tape being stolenwhere it is necessary to recover the entire backup from the memoryelement.

The data is then recovered from the memory element (step 164). This willtypically involve the output of the data (step 166) to a replacementtape. Alternatively, it may involve the uploading of data directly to aserver or via a network.

In many preferred embodiments the tape drive assembly will have atape-docking station adapted to receive, in a removable manner, a tapecassette, a tape head provided at the docking station, a non volatilememory unit, an input line, the input line being adapted to provide datasignals to the memory unit and, directly or indirectly to the tape head,the arrangement being such that in use signals input via the input lineare recorded in the memory unit as well as being directed to the tapehead for writing to the tape.

The assembly may have an output line adapted to provide output signalsof data recorded in the memory unit (e.g. for recovering data).

Tapes and tape drives have a higher, significantly higher, failure rate(when no backup/copy can be created reliably) than does, for example,hard disc memory or chip-based solid state memory. Thus a backup devicethat has a buffer memory that does not use tape is more reliable thanone that does. Tape may have failure-to-copy rate that is an order ofmagnitude, or more, or two orders of magnitude, worse than hard disc(for example).

Furthermore, storing data in a non-linear storage medium with randomaccess to the data makes it easier and faster to access just a selectedportion of data.

The invention could be thought of as backing up data to a tape drive,and also having a non-volatile memory store of the data being directedto the tape drive.

The preferred method comprises storing a backup in non-volatile memoryas a buffer in the event that there is a problem with backup to the tapedrive, in such an event data is stored to the non-volatile memory.

It is possible to store to buffer (or non-volatile memory) anyway, evenwhen the tape backup is going fine, or to store to buffer upon detectionof a problem with tape drive backup.

It will be appreciated that in one embodiment a stand alone back updevice, or unit, which has a non-volatile memory (e.g. hard drive ormemory chip) acts as a first-in-first-out buffer and data to be backedup is, upon initiation of a back up operation or routine, imported intothe device, or unit, from an external data host machine and is passedthrough the non-volatile memory, and is stored there and is passed to atape drive for writing to a back up tape.

The tape drive may be an integral part of the back up device or unit,within the same unit housing, or the tape drive may be provided in aseparate tape drive unit, and the tape drive unit and the back up unitmay be linked together. It will also be appreciated that thenon-volatile memory unit is intended to have enough capacity to storeall of the data of a typical back up routine to back up a chosen (set oramount) of data on the host machine, and that at least some, and perhapsall, of the complete set of data backed up on the non-volatile memory isoverwritten in a subsequent back up operation but is otherwise availableuntil then. This means that if there are known problems/errors with theback up to tape, then the set of data on the non-volatile memory can berecovered. For example, it could be caused to be written to a differenttape drive, or the non-volatile memory could be removable andreplaceable within another, so that the backed up data on thenon-volatile memory is preserved and not overwritten during the nextback up operation.

In one embodiment it is preferred to have the non-volatile memory unitlarge enough to store a plurality of backups of data, e.g. 2, 3, 4, 5,6, 7, or more sets. For example, it may be desirable to store at least aweek's worth of backups (e.g. daily backups). Eventually, the capacityof the non-volatile memory unit will be reached and data relating toolder backups will be overwritten by the new data from a new backupoperation in a first-in-first out manner. Thus the non-volatile memoryunit may be thought of, in some ways, as a large, possibly very large,FIFO buffer memory.

Some of the above embodiments rely upon the administrator of the back upsystem and routine being aware that the non-volatile memory is largeenough to store the desired data until it is established that the backup to tape worked correctly. It also involves a check that the back upto tape did work correctly, and if not a remedial action to be taken tomake use of/preserve the back up to non-volatile memory. This checkand/or the remedial action could be performed automatically by software.Possibly the software could check if back up to tape had executedproperly, and an alert could be provided to a human for them to initiatethe preservation/use of the data on the non-volatile back up. Thesoftware or a human can assess from time to time whether thenon-volatile memory is large enough, or whether it needs increasing. Ifit is established that the non-volatile memory needs increasing it maybe increased.

An example is a daily, or other regular, back up of system data. A backup routine may be run and this may instruct the stand-alone back up unitto perform the back up operation. Data is fed to the non-volatile memoryunit (e.g. disc, or electronic memory, or optical memory such as anoptical disc), and then on to a tape drive for storing on tape. It allgoes well and the system does not indicate to a system manager that thetape back up failed, the back up routine is simply run again the nextday (or other regular period), with previously stored data on the harddisc being overwritten by the new backup data. If there is a problem ofstoring to tape, the nonvolatile memory still has the back up data onit, not yet overwritten, and the overall data host computer/system canstill be used, changing the original data, with the back up on thenon-volatile memory. Before overwriting the back up data on thenon-volatile memory the back up data may be preserved to avoid its loss.Several days worth of backups may be kept, or a weeks worth, or severalweeks worth, or more, before the data on non-volatile memory isoverwritten and lost.

It will be appreciated that the size of the database, or data set, beingbacked up may change between different backup operations: data may beadded or deleted in use of the database. However, the overall size of alarge, commercially useful data set does not often change too quickly.There is usually time for the backup system to notice that a backupoperation is filling too large an amount of its memory capacity, and toprompt an increase in memory capacity.

Also be referring to a backup tape or a backup disc/sold state memory,it is not necessarily intended to suggest that there is only one singledisc/solid state memory or tape: more than one, or several, may beprovided and they may perform as if they were equivalent to a largermemory capacity disc/solid state device, or tape, or more than onedisc/solid state memory element.

1. A tape drive assembly for performing a backup operation, comprising:a tape-receiving station arranged to receive a data storage unitincluding a tape arranged to store data in a data backup operation; awrite head arranged to write data to said tape in a data backupoperation; a non-volatile memory unit (i) located within or (ii)removably locatable within the tape drive assembly, arranged to recorddata in a data backup operation, and arranged to communicate data tosaid write head; and an input arranged to be connected to a data hostmachine, said input being arranged to pass data to said memory unit suchthat, in use in a data backup operation, said data is communicated fromsaid data host machine to said input and is recorded in said memory unitprior to said data being passed from said memory unit to said write headfor writing to said tape.
 2. An assembly according to claim 1, whereinsaid memory unit is a magnetic disc, a solid state device, or an opticaldisc.
 3. An assembly according to claim 1, further including a redundantarray having a plurality of memory units.
 4. A method of backing up datastored on a host data-containing machine comprising the steps of: (i)receiving data from said host machine at an input of a tape driveassembly; (ii) passing said data to a non-volatile memory unit (i)located within or (ii) removably locatable within said tape driveassembly; (iii) routing said data through said memory unit and recordingsaid data in said memory unit; (iv) passing said data to a write head ofsaid tape drive assembly; and (v) writing said data to a tape datastorage unit to backup of said data to said tape data storage unit.
 5. Amethod according to claim 4, wherein said data is successfully writtenand backed up to said tape data storage unit.
 6. A method according toclaim 4, further including executing steps (ii) and (iii) substantiallysimultaneously, and executing steps (iv) and (v) substantiallysimultaneously.
 7. A method according to claim 4, further includingexecuting steps (ii) and (iii) sequentially with steps (iv) and (v). 8.A method according to claim 4, further including determining whethersaid data has been successfully written to said tape data storage unit,and recovering said data from said memory unit if it is determined thatsaid data has not been successfully written to said tape data storageunit.
 9. A method according to claim 4, further including establishing adata set to be backed up and executing steps (ii) and (iii) until all ofsaid data set to be backed up is stored in said memory unit.
 10. Amethod according to claim 4, further including mirroring said datawritten in a plurality of redundant array of memory units.
 11. A methodaccording to claim 4, wherein the method is performed in said tape driveassembly which has said memory unit as an integral unit or a combinedassembly, and which has a control processor associated with said memoryunit or said tape drive assembly, said method further comprising causingthe control processor to receive a backup operation initiation signal,the control processor causing a backup operation to be performed inresponse to receipt of said backup operation initiation signal, therebybacking up said data.
 12. A method according to claim 4, wherein a dataset to be backed up is of a generally known predetermined size, and saidnon-volatile memory unit is large enough to store all of the data from aplurality of backup operations, the method further comprising: storing aplurality of successive backup operations of said data set in saidnon-volatile memory unit; and overwriting earlier backed-up data withnew backup data in a first-in, first-out manner if there is otherwiseinsufficient capacity in said non-volatile memory unit to accommodatedata from a new backup operation.
 13. A method according to claim 4,further comprising performing a specific backup operation and ensuringthat said non-volatile memory unit has a large enough capacity to storean entire data set that is to be backed up in said backup operation. 14.A method according to claim 13, further comprising ensuring that saidnon-volatile memory unit has a large enough capacity to store at leasttwo data sets from at least two successive backup operations.
 15. Amethod according to claim 14, further including using said non-volatilememory unit as a local backup, local to said tape drive.
 16. A methodaccording to claim 14, further comprising removing said tape datastorage unit from said tape drive after completion of a first of saidbackup operations and moving said tape data storage unit geographicallyaway from said tape drive and using said tape data storage unit as aremote backup.
 17. A method according to claim 14, wherein said data sethas a smaller size than said non-volatile memory unit can store andfurther comprising writing said complete data set to said memory unit,storing said complete data set in said memory unit, and passing saiddata set to said tape drive from said memory unit in a first-in,first-out manner.
 18. A method according to claim 4, further comprisingoverwriting data previously stored in said non-volatile memory unit froman earlier backup operation with data from a later backup operation. 19.A method according to claim 4, further comprising: determining if thebackup of said data to said tape data storage unit has been achievedsuccessfully; and performing a subsequent backup operation thatoverwrites data stored in said non-volatile memory unit if the backup tosaid tape data storage unit has been achieved successfully.
 20. A methodof backing up a complete data set off a host machine including data tobe backed up, the backing up method being performed with a backup deviceseparate from said host machine, said device including a tape drivearranged to receive associated removable tape data storage units and anassociated non-volatile memory unit, the non-volatile memory unit being(i) located within or (ii) removably locatable within said tape drive,the method comprising writing data to be backed up to said non-volatilememory unit prior to writing said data to a first tape data storage unitin said tape drive in a first backup routine.
 21. A method according toclaim 20, further comprising: (iii) inserting another tape data storageunit into said tape drive; (iv) determining if data was successfullybacked up to said tape data storage unit during said first backuproutine; (v) performing a second backup routine, subsequent to saidfirst backup routine and after said data set in said host machine haschanged; and (vi) overwriting data stored in said non-volatile memoryunit during said first backup routine with a new data set from said hostmachine during said second backup routine, said second backup routinealso writing said new data set to said another tape data storage unit.22. A network comprising: a data source having a data set to be backedup; and a backup unit, said backup unit comprising a tape driveassembly, the tape drive assembly comprising a read/write head and anon-volatile memory unit, the non-volatile memory unit being (i) locatedwithin or (ii) removably locatable within the assembly, the non-volatilememory unit having a data storage capacity that can accommodate at leastone copy of said data set, said backup unit having an input forcommunicating with said data source and an output for outputting outputdata obtained from said tape drive assembly and from said memory unit,said input being arranged to communicate data coming from said datasource with said memory unit for storing said data set at said memoryunit, said memory unit being arranged to communicate with saidread/write head so as to write said data set to a tape data storage unitarranged to be located in said tape drive assembly.
 23. A tape librarycomprising: at least one tape drive and a plurality of tape data storageunits; automatic tape data storage unit location and manipulationapparatus for (a) locating said tape data storage units and (b) loadingand unloading said tape data storage units into and out of said tapedrive; a non-volatile memory unit (i) located within or (ii) removablylocatable within said at least one tape drive so as to provide a tapedrive assembly comprising: a tape-receiving station arranged to receivea tape data storage unit arranged to store data; a write head arrangedto write data to said tape data storage unit; said non-volatile memoryunit; and an input, said input being arranged to pass data to saidmemory unit such that, in use, said data is recorded in said memory unitprior to passing said data to said write head.
 24. A computer-readablemedium bearing a program which, when run on a processor of a backupsystem including both a tape drive having a tape received therein, and anon-volatile memory unit being (i) located within or (ii) removablylocatable within said tape drive, said program being arranged to causethe processor to access data being backed up during a backup routine andto copy the data to the non-volatile memory unit prior to writing thedata to the tape, in use during said backup routine.
 25. Acomputer-readable medium according to claim 24, wherein said program isarranged to cause retrieval of said data from said non-volatile memoryunit.
 26. A tape drive assembly for performing a backup operation,comprising: a tape receiving station arranged to receive a data storageunit, said data storage unit comprising a tape arranged to store data ina data backup operation; a write head arranged to write data to saidtape in a data backup operation; a non-volatile memory unit arranged torecord data in a data backup operation and arranged to communicate datato said write head; and an input arranged to be connected to a data hostmachine, said input being arranged to pass data to said memory unit suchthat, in use in a data backup operation, said data is communicated fromsaid data host machine to said input and is recorded in said memory unitprior to said data being passed directly from said memory unit to saidwrite head for writing to said tape.
 27. A tape drive assembly accordingto claim 26 wherein the non-volatile memory unit is (i) located withinor (ii) removably locatable within the tape drive assembly.
 28. A tapedrive assembly for performing a backup operation, comprising: atape-receiving station arranged to receive a data storage unit includinga tape arranged to store data in a data backup operation; a write headarranged to write data to said tape in a data backup operation; anon-volatile memory unit arranged to record data in a data backupoperation and arranged to communicate data to said write head, thenon-volatile memory unit being (i) located within or (ii) removablylocatable within the tape drive assembly; and an input arranged to beconnected to a data host machine, said input being arranged to pass datato said memory unit such that, in use in a data backup operation, saiddata is communicated from said data host machine to said input and isrecorded in said memory unit prior to said data being passed from saidmemory unit to said write head for writing to said tape, and said memoryunit being arranged to overwrite data stored on it.
 29. A tape driveassembly according to claim 28, wherein the non-volatile memory unit isarranged to act as short-term data storage.
 30. A tape drive assemblyaccording to claim 28, wherein the non-volatile memory unit is arrangedto overwrite data stored on it in a first-in, first-out manner.
 31. Atape drive assembly according to claim 28, wherein said memory unit isarranged to overwrite said data stored on it in response to the memoryunit reaching its data storage capacity.
 32. A tape drive assembly forperforming a backup operation, comprising: a tape-receiving stationarranged to receive a data storage unit including a tape arranged tostore data in a data backup operation; a write head arranged to writedata to said tape in a data backup operation; a non-volatile memory unit(i) located within or (ii) removably locatable within the tape driveassembly, arranged to record data in a data backup operation andarranged to communicate data to said write head; and an input arrangedto be connected to a data host machine, said input being arranged topass data to said memory unit such that, in use in a data backupoperation, said data is communicated from said data host machine to saidinput and is recorded in said memory unit prior to said data beingpassed from said memory unit to said write head for writing to saidtape, the non-volatile memory unit being arranged to output at least aportion of said data recorded on it upon receiving a signal indicativeof a failure in reading said data written on said tape.
 33. A tape driveassembly for performing a backup operation, comprising: a tape receivingstation arranged to receive a data storage unit including a tapearranged to store data in a data backup operation; a write head arrangedto write data to said tape in a data backup operation; a non-volatilememory unit (i) located within or (ii) removably locatable within thetape drive assembly, and arranged to record data in a data backupoperation and arranged to communicate data to said write head; an inputarranged to be connected to a data host machine, said input beingarranged to pass data to said memory unit such that, in use in a databackup operation, said data is communicated from said data host machineto said input and is recorded in said memory unit prior to said databeing passed from said memory unit to said write head for writing tosaid tape, the non-volatile memory unit being arranged to output atleast a portion of said data recorded thereupon upon receiving a signalindicative of a failure in writing said data to said tape.
 34. A methodof improving the safety of backed-up data, the method being performedwith a backup device separate from a host machine, said device includinga tape drive arranged to receive associated removable tapes and anassociated non-volatile memory unit being (i) located within or (ii)removably located within, said tape drive, the method comprising thesteps of: (a) writing data to be backed up to said non-volatile memoryunit prior to writing said data to a tape data storage unit removablylocated in said tape drive in a first backup routine; and (b) physicallyseparating the tape data storage unit and the non-volatile memory unit.35. The method of claim 34, wherein the non-volatile memory unit isremoved from the tape drive and is taken to a place remote front thebackup device.
 36. The method of claim 35, wherein the tape data storageunit is removed from the tape drive and is taken to a location remotefrom the backup device.
 37. The method of claim 34, wherein the tapedata storage unit is removed from the tape drive and is taken to a placeremote from the backup device and the non-volatile memory unit remainswithin the tape drive.